Circling behavior can be reliably produced in animals following unilateral destruction of the dopaminergic nigrostriatal pathway. This behavior is believed to be the result of an imbalance of striatal dopamine receptor stimulation. This rotating animal model has been used extensively in the investigation of the pharmacological action of numerous drugs and in the determination of the efferent pathways of motor output. During investigations in our lab on the etiology of amblyopia it became apparent that manipulation of the developing visual system may be capable of producing this circling behavior in cats. Animals were reared under various ratios of alternating monocular visual exposure during early life. Vision was restricted to one eye by the use of opaque contact lens occluders and the viewing eye was alternated according to a predetermined schedule. After two-four months of rearing some of the animals developed circling behavior averaging 30-40 spins/minute. Subsequent analysis suggests a possible role for both genetic and environmental factors. Population size is insufficient at this time, however, to warrant any conclusions. It is proposed to extend this investigation to a larger sample of cats in an attempt to evaluate both the genetic and environmental components of this behavior. An investigation of the pharmacological basis for this motor asymmetry is also proposed. The results of this proposed study may identify the current behavior as a valuable model of brain asymmetry worthy of extensive future investigation.